Streptococcus pneumoniae is an extracellular, gram-positive diplococcus that causes more deaths of adults in the United States than any other bacterium. Because of the spread of antibiotic resistant organisms, it is important to seek a greater understanding of the immune response to S. pneumoniae. The focus of this application is on the anti-bacterial response of iNKT cells, a conserved and unusual T cell subpopulation that recognizes glycolipids presented by CD1d. Recently we showed that the TCR of these cells can respond to bacterial glycolipids from gram negative bacteria. iNKT cells in mice also can provide protection from microbes that do not express glycolipid antigens that activate their TCR, this indirect response depends on cytokines from activated dendritic cells and other cell types. Studies from mice indicate that Va14/NKT cells are important for the early response to S. pneumoniae and they are critical for the survival of the infected animals. We will use CD1d tetramers to follow the response of mouse iNKT cells in vivo after S. pneumoniae infection to determine if they expand, secrete cytokines and activate other cell types. We will determine if human iNKT cells also can respond to these bacteria. Additional studies will evaluate the relative importance of bacterial antigens that activate the TCR and indirect recognition in the iNKT cell response to S. pneumoniae, by using gene-targeted mice and blocking reagents that interfere with indirect recognition. Additionally, as our preliminary data suggest that S. pneumoniae has an antigen that can activate the iNKT cell TCR, we will purify this antigen and determine its structure. The results from these studies should help in understanding iNKT cell biology and the response to S. pneumoniae, which could lead to the development of more effective vaccines against this organism. [unreadable] [unreadable] [unreadable] [unreadable]